It is permissible if somebody says, "I give this slave-girl to you for your service. ..."

Narrated Abu Huraira:

Allah's Apostle ﷺ said, "The Prophet Abraham migrated with Sarah. The people (of the town where they migrated) gave her Ajar (i.e. Hajar). Sarah returned and said to Abraham, "Do you know that Allah has humiliated that pagan and he has given a slave-girl for my service?"

حَدَّثَنَا أَبُو الْيَمَانِ، أَخْبَرَنَا شُعَيْبٌ، حَدَّثَنَا أَبُو الزِّنَادِ، عَنِ الأَعْرَجِ، عَنْ أَبِي هُرَيْرَةَ ـ رضى الله عنه ـ أَنَّ رَسُولَ اللَّهِ ﷺ قَالَ " هَاجَرَ إِبْرَاهِيمُ بِسَارَةَ، فَأَعْطَوْهَا آجَرَ، فَرَجَعَتْ فَقَالَتْ أَشَعَرْتَ أَنَّ اللَّهَ كَبَتَ الْكَافِرَ وَأَخْدَمَ وَلِيدَةً ". وَقَالَ ابْنُ سِيرِينَ عَنْ أَبِي هُرَيْرَةَ عَنِ النَّبِيِّ ﷺ " فَأَخْدَمَهَا هَاجَرَ ".